This invention relates to bladeless shearing of linear stock such as steel tubing and, more particularly, to a supported shear apparatus having a reversible drive and to a method of operating same to improve the quality of the newly created stock ends at each parting plane.
In U.S. Pat. No. 4,635,514 xe2x80x9cElliptical Shearing Apparatusxe2x80x9d, issued Jan. 13, 1987 to Alexander Borzym, there is disclosed a bladeless device for shearing linear stock, such as bar stock and tubing, by causing a section of the stock to translate laterally through an elliptical shaped orbital path relative to the axially adjacent stock. As is more fully disclosed in the aforesaid patent, this is achieved through the use of a first body referred to as a xe2x80x9cdie holderxe2x80x9d having a central, die-like aperture formed therein which is adapted to receive and precisely surround the linear stock. One side of the die holder is pinned to permit pivotal and limited lateral motion. The other side is connected to a drive mechanism consisting of a large electric motor driving a flywheel at constant speed and a clutch and brake mechanism for selectively and momentarily imparting orbital motion to the die holder. Orbital motion of the die holder around the mechanical drive center produces a unidirectional, elliptical translation of the stock receiving die which lies between the drive center and the pinned end of the die holder. The amplitude of the elliptical motion is a function of the amplitude of the orbital drive motion and the geometric location of the die within the die holder body.
By placing a fixed die also having a stock-receiving aperture immediately axially adjacent to the moveable die, a scissors-like shearing action is produced on a length of stock which is inserted through the two aligned dies; the shear line is defined by the mating plane of the two dies. Deformation of tubular stock is prevented by placing a special mandrel in the stock in the area of the shear plane.
There are numerous advantages to a shear of this type relative to cutoffs using blades or other cutting implements. The principal advantages are the elimination of the cutting implement as a perishable component and the conservation of material in the work piece; i.e., saw blades and guillotine blades remove a section of material approximately equal to the thickness of the blade each time it passes through the stock. The resulting loss of material from the stock is significant, particularly where short lengths and high cutting rates are employed.
A first aspect of my invention is the provision of an improved drive for the orbital die, which drive eliminates the need for the clutch and brake of the ""514 patent. In general, my improved drive comprises an hydraulic power source for moving the orbital die in opposite directions. Preferably, the power source comprises two separate hydraulic cylinders connected to respective linear racks engaging the opposite sides of a pinion connected to displace the orbital die.
A second aspect of my invention includes a method of shearing tubular stock by (a) setting the stroke to approximately the wall thickness of the stock, (b) orbitally displacing the moveable die 270 degrees from a home position, and (c) orbitally displacing the moveable die back to the home position.
These and other advantages of the invention will be best understood by reading the following specification which described an illustrative embodiment of the invention in detail.